(1) Field of the Invention
The present invention relates to a system for technically realizing copyright protection of digital production, and especially relates to copyright protection technologies in replaying and recording contents that are digital production.
(2) Description of the Prior Art
Due to the recent development of Internet-related technologies, it is possible to distribute contents such as music through the Internet and to receive charges from the users who have downloaded distributed contents.
On the other hand, digital production that have been downloaded on personal computers through the Internet can be easily duplicated. In order to prevent unauthorized duplication, for instance, encryption technologies are used.
When a content for sale is provided through the Internet, the sample of the content with a lower quality may be also provided for sales promotion. For instance, users are supposed to purchase a content after trying the free sample of the content.
In this case, since the provider wants the sample to be tried by as many as users and clients, it is desirable that the sample can be replayed by personal computers connected to the Internet as the hardware. Note that in some cases, the provider may want control the distribution and replay of the sample to some extent, so that the content of the sample is assumed to be encrypted.
However, if the content for sale and the content of the sample are encrypted in the same encryption system and provided through the Internet in response to the request, the content for sale is equally vulnerable to fraudulent acts such as analysis of the encryption algorithm as the content of the sample.